Extreme pressure properties of synthetic lubricants

ABSTRACT

EXTREME PRESSURE PROPERTIES OF SYNTHETIC LUBRICANTS, E.G., ESTERS, ARE IMPROVED BY THE ADDITION OF (A) DIBROMINATED NEOPENTYL GLYCOL ESTER, (B) A PHOSPHATE ESTER, (C) A POLYCARBOXYLIC ACID HAVING 2-54 CARBON ATOMS, OR (D) COMBINATIONS OF (A), (B) AND (C).

United States Patent Oflice 3,701,730 Patented Oct. 31, 1972 3,701,730 EXTREME PRESSURE PROPERTIES OF SYNTHETIC LUBRICANTS David A. Daniels, Kendall Park, and Kenneth T. Wendler, Freshold, N.J., assignors to W. R. Grace & C0., New York, N.Y. No Drawing. Filed Dec. 23, 1970, Ser. No. 101,098 Int. Cl. C10m l/46, 1/30 U.S. Cl. 25249.9 8 Claims ABSTRACT OF THE DISCLOSURE Extreme pressure properties of synthetic lubricants, e.g., esters, are improved by the addition of (a) dibrominated neopentyl glycol ester, (13) a phosphate ester, a polycarboxylic acid having 2-54 carbon atoms, or

(d) combinations of (a), (b) and (c).

This invention is the improvement of extreme pressure properties of synthetic lubricants.

With the advent of powerful jet engines there has come the need for lubricants which are able to withstand the tremendous pressure to which they are subjected without losing their lubricating properties. The Timken Test as is well-known in the art, involves apparatus known as the Timken Extreme Pressure Tester. In the test the tester is operated with a steel test cup rotating against a steel test block. The rotating speed is 405.88+2.54 rt/min. which is equivalent to a spindle speed of 800: r.p.m. Fluid samples are preheated to 100:5 F. before starting the test. Two determinations are then made: the minimum load (i.e., score value) which will rupture the lubricant film being tested between the rotating cup and the stationary block and cause abrasion, and the maximum load (OK value) at which the rotating cup will not rupture the lubricant film between the rotating cup and the stationary block and cause abrasion. This method of testing pressure properties of lubricants is widely used in the art.

The lubricants for which we have developed improvements in extreme pressure properties are used typically in jet engines, automobile engines, gear oils, and the like.

Some of the requirements for extreme pressure properties have become progressively more rigid but unfortunately the lubricating industry has been unable to keep pace with the needs brought about by the development of more severe operating conditions. A typical breakdown in the lubricant will cause engine overheating, thereby increasing wear and tear on the engine. In severe cases a breakdown in the lubricant will cause the lubricant to practically solidify within the engine, causing severe damage.-

Suitable synthetic lubricant base stocks for the practice of the invention are esters of alcohols having 1 to 20, especially 4 to 12 carbons and aliphatic carboxylic acids having from 3 to 20, especially 4 to 12 carbons. The ester base may comprise a simple ester (reaction product of a monohydroxyalcohol and a monocarboxylic acid), a polyester (reaction product of an alcohol and an acid, one of which has more than one functional group), or a complex ester (reaction product of a polyfunctional acid with more than one alcohol, or of a polyfunctional alcohol with more than one acid). Also, excellent synthetic lubricants may be formulated from mixtures of esters, such as major proportions of complex esters and minor amounts of diesters.

Monohydric alcohols suitable for making ester base stocks include methyl, butyl, isooctyl, dodecyl and octadecyl alcohols. Oxo alcohols prepared by the reaction of ole-fine with carbon monoxide and hydrogen are suitable. Neo alcohols, i.e., alcohols having no hydrogens on the beta carbon atom are preferred. Examples of such alcohols are 2,2,4trimethyl-pentanol-1 and 2,2-dimethyl propanol.

Polyalcohols used for the production of base oil esters preferably contain 1 to 12 carbons. Examples of dialcohols are 2-ethyl-1,3-hexanediol 2-propyl-3,3-heptanediol, 2-butyl-l,2-butanediol, 2,4-dimesityl-1,3-butanediol, and polypropylene glycols having molecular weights of from about to 300. Alcohols having 3,4,5 or more hydroxyl groups per molecule are also suitable. Examples of these polyols are pentaerythritol, dipentaerythritol, and trimethylolpropane. Mixtures of alcohols may also be used.

Suitable carboxylic acids for making the ester base oils include monoand dibasic aliphatic carboxylic acids. Examples of appropriate acids are butyric, valeric, sebacic, azelaic, suberic, succinic, caproic, adipic, ethyl suberic, diethyl adipic, oxalic, malonic, glutaric, pentadecanedicarboxylic, diglycolic, thiodiglycolic, acetic, propionic, caprylic, lauric, palmitic, pimelic and mixtures thereof. Preferred acids are sebacic, azelaic, glutaric, adipic, and their mixtures.

Examples of suitable ester base oils are ethyl palmitate, ethyl laurate, butyl stearate, di-2-ethylhexyl sebacate, di- 2-ethylhexyl azelate, ethyl glycol dilaureate, di-2-ethylhexyl phthalate, diisooctyl sebacate, bis-(tridecyl) adipate, di-(1,3-methylbutyl) adipate, di-(l-ethylpropyl) azelate, diisopropyloxylate, dicyclohexyl sebacate, glycerol tri-nheptoate, di(undecyl) azelate, and tetraethylene glycol di- (2-ethylene caproate), and mixtures thereof. An especially preferred mixture of esters consists of about 50-80% wt. bis(2,2,4-trimethylpentyl) azelate and 20 to 50% 1,1-trimethylyl propane triheptanoate.

Especially preferred esters for use as base stocks in the present invention are esters. of monocarboxylic acids having 3 to 12 carbons and polyalcohols such as pentaerythritol, dipentaerythritol and trimethylolpropane. Examples of these esters are pentaerythrityl tetrabutyrate, pentaerythrityl tetravalerate, pentaerythrityl tetracaproate, pentaerythrityl dibutwratedicaproate, pentaerythrityl butyrate-caproate divalerate, pentaerythrityl butyrate trivalerate pentaerythrityl butyrate tricaproate, pentaerythrityl tributyrate-caproate, mixed C saturated fatty acid esters of pentaerythritol, dipentaerythrityl hexavalerate, dipentaerythrityl hexacaproate, dipentaerythrityl hexaheptoate, dipentaerythrityl hexacaprylate, dipentaerythrityl tributyratetricaproate, dipentaerythrityl trivalerate trinonylate, dipentaerythrityl mixed hexaesters of C fatty acids and trimethylolpropane heptylate. Pentaerythrityl esters of mixtures of C acids are excellent base oils.

Esters which enable the above stated base stocks to exhibit improved extreme pressure properties by this invention include esters prepared from straight chain monobasic alkanoic acids having 2-36-(preferably 4-18) carbon atoms and a dibrominated neopentyl glycol having the following formula:

CHzBr Other acids which are useful in addition to those straight chain acids mentioned above include the neoacids represented by the following structure:

wherein R is hydrogenor an alkyl radical containing from 1-6 carbon atoms, n is an integer from -8 and R and R" are alkyl radicals containing 1-3 carbon atoms.

It is, therefore, an object of this invention to provide a lubricant which exhibits improved extreme pressure properties. It is a further object to increase the extreme pressure properties of synthetic lubricantshaving an ester base. It is still a further object to improve the extreme pressure properties of synthetic lubricants which find use in jet engines, gears and in automobiles and the like. It is a further object of this invention to improve the extreme pressure properties of multipurpose oils and lubricants.

We have found, therefore, that when a member of the group consisting of, halogen containing esters, phosphate esters, and aliphatic polycarboxylic acids, having 2-18 preferably 4-18 carbon atoms e.g. adipic, azelaic, sebacic, and dimers andtrimers thereof orcombinations of group members (such that a total of 54 carbon atoms may be present in the trimer acid of a polycarboxylic acid having 18 carbonatoms) is added to a lubricant, the lubricant exhibits improved extreme pressure properties. For purposes of the specification and claims, dimers and trimers are defined as defined in The Condensed Chemical vDictionary, 5th ed., Reinhold Publicating Corporation, New York (1956). It is stated therein that a dimer is a molecule formed by union of two identical simpler molecules and a trimer is a molecule formed by union of three identical simpler molecules.

More specifically, a typical lubricant base stock, bis(tridecyl) adipate (C H OOC(CH COOC H exhibits a Timken OK load of 6 pounds. However, when a lubricant is prepared comprising 10 parts by weight of the same lubricant base stock (bis(tridecyl) adipate) and 1 part by weight of" a dibrominated neopentyl glycol ester, said ester having the formula 0 0mm 0 cnlonooom-b-omol a-(cnl -cni H Br A wherein n is an integer in the range of 0-20, and subjected to, the Timken Test, a Timken OK load of 24 pounds is obtained. (For purpose of this specification and claims, reference to dibrominated neopentyl glycol diheptanoate refers to the structure having the formula given above where n=5.) Although We prefer to use dibrominated neopentyl glycol diheptanoate in a ratio of 10 parts to 100 parts lubricant base stock by weight,we have found that 5-30:100 parts by. weight also imparts improved extreme pressure properties.

We have alsofound that a lubricant comprising the same lubricant base stock bis(tridecyl) adipate, dibrominated neopentyl glycol dipheptanoate of the type listed supra, and a free polycarboxylic in a parts by weight ratio of about 100:5 to 30:0.005 to 0.2, preferably about 100 parts by weight base stock: 10 parts by weight halogenated ester:0.03 parts by weight polycarboxylic acid will exhibit a Timken OK load of pounds. We prefer to use a trimer, C acid described supra (i.e. 3 molecules of an acid, having 18 carbon atoms have united to form the molecule having 54 carbon atoms), but have found that the other polycarboxylic acids listed supra are also quite operable.

We have also found that phosphate esters of the formula:

where R, is an .aryl group having 6-12 carbon atoms, an alkyl group having 1 to 10 carbon atoms, an aralkyl'group having 7-22 carbon atoms or an alkaryl group having 7-22 carbon atoms, imparts improved extreme pressure properties to the lubricant base stock when admixed with the lubricant in a parts by weight ratio of lubricant base stockzphosphate ester of 100:0.5-5. We have found that a particularly effective phosphate ester is tricresyl phos- 4 phate. Other particularly useful phosphate esters include cresyl diphenyl phosphate ester, tn'phenyl phosphate ester, trioctyl phosphate ester, and diphenyl octyl phosphate ester. A thus prepared lubricant will thereby provide a Ti-mken OK load value of about 9 pounds, or about 50% better than a lubricant without the phosphate ester.

We have further found that when both the polycarboxylic acid, and a phosphate ester are admixed with a typical lubricant base stock, e.g., bis(tridecyl) adipate, the Timken 0K load value is increased as much as 50%. When preparing such a lubricant we prefer to use (in parts by weight) parts lubricant base stockz3 parts phosphate ester:0.03 part polycarboxylic acid, although a range, in parts by weight, of lubricant base stockzphosphate esterzdicarboxylic acid of 10020.5 to 520.002 to 0.2 is also operable.

We have further found that when a halogenated ester and a phosphate esterv are added to the lubricant base stock the Timken OK load value can be increased as much as We prefer to use 100 parts by weight lubricant base stock: 10 parts by weight halogenated ester. However, parts by weight ratios in the range of 100:0.5 to 5:5 to 30 (lubricant base stockzphosphate esterzdibrominated neopentyl glycol diheptanoate) also produces excellent results.

In another embodiment of our invention a typical lubricant base stock, e.g., bis(tridecyl) adipate, is admixed with dibrominated neopentyl glycol diheptanoate, a phosphate ester, and a polycarboxylic acid, preferably in a parts by weight ratio of 100 parts lubricant base stock: 10 parts dibrominated neopentyl glycol diheptanoate:3 parts phosphate ester:0.03 part polycarboxylic acid. Operable ratios in parts by weight of lubricant base stockzdibrominated neopentyl glycol diheptanoatezphosphate esterzpolycarboxylic acid are 100:5-30:0.5-5:0.0020.2. We have found that when the thus described composition is subjected to the Timken Test a Timken OK load value of 35 pounds, or nearly 600% as much as when only the lubricant base stock is subjected to the test, can be obtained.

In a preferred embodiment of this invention bis(tridecyl) adipate is used as lubricant base stock to prepare a lubricant with improved extreme pressure properties. Said ester is preferably admixed with the following additives in parts by weight as follows:

100 lubricant base stock (e.g., bis(tridecyl) adipate) 3 phosphate ester (e.g., tricresyl phosphate) 10 dibrominated neopentyl glycol diheptanoate 0.03 polycarboxylic acid having 2-54 carbon atoms 0.5 antioxidants, corrosion inhibitors, antifoamants, viscosity index improvers, demulsifiers, emulsifiers, and the like.

When this lubricating composition is subjected to the Timken Test a Timken OK load value of about 50 pounds is obtained. (The additives which may be used include antioxidants, e.g. p,p'-dioctyldiphenylamine; corrosion inhibitors, e.g. high molecular Weight dicarboxylic acids; antifoamants; and the like. (See Encyclopedia of Chemical Technology, 2nd ed., John Wiley & Sons (1965), vol. 6, pp. 317-346 and vol. 2, pp. 588-603.) Preferably the additives comprise 0-10 parts by weight of the total composition.)

Although the above stated composition is the preferred embodiment of our invention, any of the aforementioned dibrominated neopentyl glycol diheptanoate, phosphate esters, and/or polycarboxylic acids can be used.

The following examples will aid in explaining the invention without intending to limit it.

EXAMPLE 1 A commonly used base stock lubricant, bis(tridecyl) adipate was subjected to the heretofore described Timken Test as follows. The lubricant was placed in the test cup and block of the Timken apparatus and when the sump was about half-filled with the fluid the motor was started.

After a break in period of about 30 seconds, the machine was allowed to run for another 10 minutes at a load of 3 pounds. When it was found that the lubricant could withstand said weight (3 lbs.), the load was gradually increased with fresh lubricant until it was found the OK load value of 6 pounds.

EXAMPLES 2-10 Example 1 was repeated substituting the following lubricants for the bis(tridecyl) adipate with substantially similar results:

isooctylisodecyl adipate (Example 2) di-2-ethylhexyl adipate (Examples 3) diisooctyl sebacate (Example 4) C C pentaerythritol ester/w. (Example 5) diisodecyl adipate (Example 6) C -C trimethylolpropane ester (Example 7) di-2-ethylhexyl azelate (Example 8).

EXAMPLE 9 A composition consisting essentially of 100 parts by weight bis(tridecyl) adipate, 10 parts dibrominated neopentylglycol diheptanoate, and 0.01 part sebacic acid was thoroughly mixed and subjected to the Timken Test as described in Example 1. A Timken OK load value of pounds was obtained.

EXAMPLES 11-12 Example 10 was repeated except that adipic acid (Example 11) and azelaic acid (Example 12) were substituted for the sebacic acid. Timken OK load values of 15 pounds were obtained in each instance.

EXAMPLE 13 A composition consisting essentially of 100 parts by weight bis(tridecyl) adipate was admixed thoroughly with 10 parts by weight dibrominated neopentylglycol diheptanoate and 3 parts by weight tricresyl phosphate and subjected to the Timken Test as described in Example 1. A Timken OK load value of 15 pounds was obtained.

EXAMPLES 14-16 Example 13 was repeated with similar results except that:

cresyldiphenyl phosphate (Example 14) triphenyl phosphate (Example 15), and trinonylphenyl phosphate (Example 16) were used instead of the tricresyl phosphate.

EXAMPLE 17 100 parts by weight bis(tridecyl) adipate, 3 parts by weight tricresyl phosphate and 0.01 part by weight sebacic acid were thoroughly mixed and subjected to the Timken Test in Example 1. A Timken OK load value of 9 pounds was obtained.

EXAMPLES 18-19 Example 17 was repeated except that adipic .acid (Example 18) and azelaic acid (Example 19) were substituted for the sebacic acid; the results, in each instance, were substantially identical with those obtained in Example l7.

EXAMPLE 20 A homogeneous composition containing 100 parts by weight bis(tridecyl) adipate, 3 parts by weight tricresyl phosphate, 10 parts by weight dibrominated neopentylglycol diheptanoate and 0.01 part by weight sebacic acid EXAMPLE 21 This example illustrates the improved extreme pressure properties that can be attained by this invention.

A technical grade pentaerythrital ester made from a mixture of C -C acids (said acids being, valeric, hexanoic, heptanoic, octanoic, isovaleric, decanoic, nononoic was used as the base stock to prepare a typical lubricant which is commonly used in engines of various types. This was then divided into 3 portions. The first portion designated Lubricant A, was subjected to the Timken Test and an OK load value of 6 pounds was obtained.

3-parts by weight tricresyl phosphate and 0.005 part by weight sebacic acid were added to parts of the second portion thoroughly mixed, and labeled Lubricant B. When subjected to the Timken Test it was found that an OK load value of 9 pounds was obtained.

10 parts by weight dibrominated neopentylglycol diheptanoate, 3 parts by weight tricresyl phosphate, and 0.005 part by weight sebacic acid were added to 100 parts of the third portion, thoroughly mixed, labeled Lubricant C, and then subjected to the Timken Test. A Timken OK load value of 35 pounds were attained.

EXAMPLE 22 A composition consisting essentially of 100 parts by 'weight bis(tridecyl) adipate, 10 parts dibrominated neopentylglycol diheptanoate, and 0.028 part of a trimer C acid were thoroughly mixed and subjected to the Timken Test as described in Example 1. A Timken OK load value of 15 pounds was obtained.

EXAMPLE 23 A composition consisting essentially of 100 parts by weight bis(tridecyl) adipate, 3 parts by weight tricresyl phosphate, and 0.028 part by weight of the trimer C acid were thoroughly mixed and subjected to the Timken Test as described in Example 1. A Timken OK load value of 6 pounds was obtained.

EXAMPLE 24 The composition of Example 23 was again prepared and admixed with 10 parts by weight dibrominated neopentylglycol diheptanoate and subjected to the Timken Test as described in Example 1. A Timken OK load value of 50 pounds was obtained.

EXAMPLE 25 The composition of Example 23 was again prepared and admixed with 5 parts by weight dibrominated neopentylglycol diheptanoate and subjected to the Timken Test as described in Example 1. A Timken OK load value of 18 pounds was obtained.

EXAMPLES 26-27 Example 1 was repeated except that the dibrominated neopentyl glycol diheptanoate was replaced with dibrominated neopentyl glycol dibutyrate (Example 26) and dibrominated neopentyl glycol distearate (Example 27). Similar results were obtained.

What is claimed is: r

1. In an extreme pressure lubricant comprising a major amount of an ester base oil selected from the group consisting of bis(tridecyl) adipate, ethyl palmiate, ethyl laurate, butyl stearate, di-2-ethylhexy1 sebacate, di-2- ethylhexyl azelate, ethyl glycol dilaureate, di-Z-ethylhexyl phthalate, diisooctyl sebacate, di(l,3-methyl'butyl) adipate, di-(l-ethylpropyl) azelate, diisopropyl oxylate, dicyclohexyl sebacate, glycerol tri-n-heptoate, di(undecyl) azelate, and tetraethylene glycol di-(Z-ethylene) caproate,

and mixtures hereof, the improvement comprising the presence of a dibrominated neopentyl glycol ester having the formula wherein n is an integer in the range of -20, the weight ratio of ester baseoil-:to dibrominated neopentyl glycol ester being 100:10-30.

2. The extreme pressure lubricant of claim 1 in which the ester base oil is bis(tridecyl) adipate.

3. The extreme pressure lubricant of claim 1 in which the dibrominated neopentyl glycol ester is dibrominated neopentyl glycol diheptonoate.

4. In an extreme pressure lubricant comprising a major amount of an ester base oil selected from the group consisting of bis(tridecyl) adipate, ethyl palmitate, ethyl laurate, butyl stearate, di-Z-ethylhexyl sebacate, di-Z-ethylhexyl azelate, ethyl glycol dilaureate, di-2-ethylhexyl phthalate, diisooctyl sebacate, di-(1,3-methylbutyl) adipate,;di-(1-ethylpropyl) azelate, diisopropyl oxylate, dicyclohexyl sebacate, glycerol tri-n-heptanoate, di(undecyl) azelate, and tetraethylene glycol di-(2-ethylene) caproate,

and mixtures thereof, the improvement comprising the presence of; (a) a dibrominated neopentyl glycol having the formula wherein n is an integer in the range of 0-20; (b) a phosphate ester selected from the group consisting of tricresyl phosphate, cresyldiphenyl phosphate, triphenyl phosphate, trioctyl phosphate, diphenyloctylphosphate, and trinonylphenyl phosphate; and (c) an aliphatic polycarboxylic acid having 2-54 carbon atoms, the weight ratio of ester base oil to dibrominated neopentyl glycol ester to phosphate ester to aliphatic polycarboxylic acid being :5-30:0.55:0.0020.28.

5. The extreme pressure lubricant of claim 4 in which the ester base oil is bis(tridecy1) adipate.

6. The extreme pressure lubricant of claim 4 in which the dibrominated neopentyl glycol ester is dibrominated neopentyl glycol diheptonate.

7. The extreme pressure lubricant of claim 4 in which the phosphate ester is tricresyl phosphate.

8. The extreme pressure lubricant of claim 4 in which the aliphatic polycarboxylic acid is sebacic acid, adipic acid, azeolaic acid, a dimer C acid, or a trimer C acid.

References Cited UNITED STATES PATENTS 2,938,871 5/1960 Matuszak et al. 252-49.9 3,579,449 5/1971 Wann et al. 25249.9 3,260,672 7/ 1966 MacPhail et a1 25254.6

DANIEL E. WYMAN, Primary Examiner W. H. CANNON, Assistant Examiner US. Cl. X.R. 252-56 R, 56 S 

